Powder metallurgy is a technology which use metal powders as raw materials, manufacturing metal materials, composite materials and others by forming and sintering technology. Iron powders has been widely used as a vital metal powders's raw materials in powder metallurgy industry. However, with the development of science and technology, people need high performance powder metallurgy materials. So it need to develop high performance iron-based alloyed powders as well as pure iron powders.
The iron-based alloyed powders, being its uniform structure and composition, have been widely used in powder metallurgy materials for decreasing sintering temperature and improving the mechanical properties. There are many manufacturing methods for iron-based alloyed powders such as chemical co-precipitation-co-reduction, atomization, mechanical alloying, electrolytic process etc. Chemical co-precipitation-co-reduction can produce the powders beneath 10 micrometers, which has good liquidity, compactibility and sintering character. However, chemical co-precipitation-co-reduction is complicated, high cost and its products is expensive. Start elements are melted in a medium frequency induction furnace, then high pressure atomized medium water or gas through a atomizing nozzle to smash stream of molten metal, and then the smashed liquid drop take shape of solid particle after refrigeration to obtain the pre-alloyed powders. The alloyed powders produced by atomization have the high alloying extent, good sintering character, low cost of production, but poor compactibility, poor particle distribution and high oxygen content. Iron-based alloyed powders prepared by mechanical alloying and electrolytic also have disadvantage. Therefore, it is very significant to seek for a simple, low cost, and pollution-free process to prepare iron-based alloyed powders.
Iron-based grinding waste contains many iron-based alloyed powders. However, it is difficult to be reused for the abrasive, grinding wheel additives and many iron-based alloyed powders embedded with each other. Iron-based grinding waste are usually piled up results in occupying space, polluting the environment.
SHS (Self-propagating High-temperature Synthesis) is a new technology for preparing materials with the heat from exothermic chemical reaction itself. In fact, SHS is a redox reactions, which aluminum and iron oxide occur oxidation-reduction reactions and obtain high temperature. Reaction products of iron and aluminum oxide will alloy immediately. If centrifugal force is added together with redox reactions, alumina will distribute in the inner surface of the steel pipe, and iron will distribute in the between steel pipe and alumina ceramic layer for the density difference of alumina and iron.
At present, the research and patents of SHS steel pipe are focused on the type of additives and its quantities and the control of materials cost. For example, Chinese Patent 90107244.3 describes a method of manufacturing corrosion resistant and friction resistant ceramic SHS steel pipe. In the process, the additive is SiO2 and one or two kind of alkali metal oxides (Na2O K2O Li2O) and one or two kind of alkaline-earth metallic oxides (MgO CaO BaO). Then the additive is added with Al+Fe2O3 (or Fe3O4). Chinese Patent 200510136673.0 describes that the materials mainly include Al Fe2O3 and accessory SiO2, feldspar fine powders, quartz fine powders, fluorite fine powders and 0.5-1.5 wt % Al2O3 for manufacturing ceramic composite steel pipe. The materials are acid slag, Al and SiO2 is known for preparing ceramic-lined steel pipe, as described in Chinese patent 01139227.4.
In this invention, aluminum powders and iron-based alloyed powders recycled from iron-based grinding waste can be as raw materials used in SHS lined steel pipe. Compared with Chinese patents 90107244.3 and 200510136673.0, the raw materials is iron-based alloyed powders, instead of Fe2O3 (or Fe3O4) powders. It can reduce the cost of SHS lined steel pipe. Compared with Chinese patent 01139227.4, iron-based alloyed powders have higher total iron content than acid slag. In addition, iron-based alloyed powders contain some Al2O3 and SiO2, which can be melted in SHS and control the high temperature, to increase the thickness of ceramic layer in SHS steel pipe to prevent steel pipe from deformation. SiO2 can decrease the crystallization temperature of Al2O3 primary phase and increase ceramic melt time and promote gas phase escaping. So this invention can enhance the quality of ceramic layer.
Structural component mainly participates in machine operation, bearing tension, compression, torsion, impaction, and other combined stress, and rubbing against dual component. Powder metallurgy technology can manufacture near fine form widely used iron-based structural components using iron powders and its alloyed powders.
At present, most references and patents focus on the improvement of alloy recipe, preparing alloyed powders described in above-mentioned. Chinese patent 200710098524.9 describes a method for preparing high-performance iron-based alloyed powders used in laser welding, adapting precipitation precursor reduction and mechanical alloying process. In addition, some scholars try to improve the present preparation method in decreasing the materials cost terms. Chinese patent 200510048519.8 describes cryogenic treatment process under −50° C. to −198° C., and thereafter smashing alloy to massive of diameter 3˜5cm by the inert-gas protection jaw crusher, then grinding to the required granularity by the inert-gas protection ball grinding mill with sieve. This method can obtain alloyed powders at low finished cost, and its cost just is 1.1˜1.3 times of metal materials. Chinese patent 200910043135.5 describe a process for manufacturing cobalt pre-alloyed powders by recycling synthesized diamond waste powders accelerant and other secondary metal, adding some iron and cobalt, electrolyzing and hydrogen reducing. However, no references and patents describe a method for recycling iron-based alloyed powders from iron-based grinding waste.
This invention describes a process for recycling iron-based alloyed powders from iron-based grinding waste and for using in SHS lined steel pipe, powder metallurgy structural component, magnetic grinding, thermal spray with the iron-based alloyed powders. It is suitable for recycling economy.
Magnetic grinding is a new machining technology which can machine high precision components. Magnetic abrasive is grinding the surface of components when the moving magnetic field is being applied. It has many advantages such as three-dimensional grinding, high accuracy, small deformation, less temperature rising and high efficiency. Magnetic abrasive mainly consists of matrix and abrasive grains.
Magnetic abrasive is made from ferro-magnetic materials and abrasive grains as described in references and patents. Chinese patent 200710075464.9 describes a magnetic abrasive made from steel needle (diameter 0.5 mm˜2 mm, length 5 mm˜20 mm), steel ball (diameter 0.5 mm˜2 mm), ceramic powders (corundum, kaolin, micro silica powders). A special structure of magnetic abrasive is core-shell structure, which the core is granulated magnetic materials and the shell is a ceramic coating or a plastic coating, as described in Chinese patent 200810031570.1. This kind of magnetic abrasive can improve the machining efficiency. Chinese patent 00136573.8 describes a method for preparing magnetic abrasive by hot-press sintering. The raw materials is iron powders, brown corundum powders, white corundum powders, CBN, diamond micro-powders and other ultra-hard abrasive. However, there is no report about preparing magnetic abrasive based on iron-based grinding waste.
Thermal spray is a surface strengthening technology, by heating the powders or filiform metal materials or nonmetal materials to molten or semi-molten by some kind of heat producer (such as voltaic arc, plasma spray or blaze, etc), then spraying it to pretreated matrix's surface at a certain speed by means of flame flow itself or compressed air, depositing and then forming surface coating with various function.
Thermal spray powders play an important role among thermal spray materials. There are two methods for preparing thermal spray powders. One is mixture of element powders, the other is pre-alloyed powders. Thermal spray pre-alloyed powders includes Ni-based, iron-based and Co-based alloyed powders.
Ni-based self-fluxing alloyed powders consists of chromium, boron, silicon, carbon, copper, molybdenum etc. alloyed powders are widely applied in self-fluxing spray welding alloyed powders for its low melting point, good self-fluxing, anti-corrosion, anti-friction, heat-resistance, anti-oxidation and so on. There are two kinds of iron-based alloyed powders, one is stainless steel type, which include major nickel and chromium; the other is high-chromium iron type, which includes major chromium and carbon. Co-based self-fluxing alloyed powders, which consist of chromium, tin, nickel, boron, silicon, etc, has a good properties of high-temperature behavior, red hardness, anti-friction and anti-oxidation.
Ni-based and iron-based thermal spray alloyed powders are shown in table 1.
TABLE 1MarkCBSiCrFeCoNiWMoNi-25≦0.21.0~2.03.0~4.5—≦8 —bal.——Ni-450.3~0.71.5~3.52.5~4.514~17≦148~16bal.——Ni-600.6~1.02.4~4.53.0~5.014~17≦15—bal.——Fe-300.3~0.61.5~2.52.5~3.510~16bal.—26~32——Fe-400.1~0.21.5~2.51.5~2.517~19bal.1~2 7~91~21~2
There are three advantages of iron-based alloyed powders recycled from processing iron-based grinding waste Ni60 mixture powders used in thermal spray. First, iron-based alloyed powders contains lots of alloy elements such as Cr, Ni, Mo, Mn etc. Second, iron-based alloyed powders contains some micro abrasive. During thermal spraying, abrasive grains and iron-based grains will drop out since they embed with each other and distribute more uniformly. So it has good anti-friction. Third, the melting point is not high and beneficial to coating and matrix can combine better.